tvb_composite problem

Hello,

I have the following problem. My dissector needs to rebuild a new tvb. A better description would be, I need to cut out some data and send it to the next dissector.

As Example....

02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02
02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02
11 11 11 11 11 11 22 22 22 22 22 22 33 33 44 44             I
10 01 00 00 00 aa c2 bc cd ef ed fe 15 18 1d d2
44 44 44 44 44 44 44 44 44 44 44 44 44 44 44 44            II
10 01 00 00 00 aa c2 bc cd ef ed fe 15 18 1d d3
....

the first to lines are some other protocol data (my protocol) 11, 22 and 33 are the ethernet header 44 the ip header

what I now need to do is to cut out line I and II, reasamble it an send it to the next dissector (ethernet). I found the solution in building a composite buffer. The real code looks a little bit different but for the data above it would like this.

tvbuff_t *new_tvb;
tvbuff_t *tvb_sub1;
tvbuff_t *tvb_sub2;
new_tvb = tvb_new_composite();
tvb_sub1 = tvb_new_subset(tvb, 32, 16, 16);
tvb_sub2 = tvb_new_subset(tvb, 64, 16, 16);
tvb_composite_append(new_tvb, tvb_sub1);
tvb_composite_append(new_tvb, tvb_sub2);
tvb_composite_finalize(new_tvb);
call_dissector(handle_eth, timing_tvb, pinfo, tree);

The handle_eth is set with

handle_eth = find_dissector("eth");

No the problem…. With Ethernet everything is fine. Then the Ethernet dissector sends it to IP dies because of wrong data. When I look at the data IP gets I see that IP do not get the right data. It should be

  44 44 44 44 44 44 44 44 44 …..

but it is

 44 10 01 00 00 00 aa c2 …..

That shows me that the composite buffer is not working the right way. I found some old mailing lists entries (the newest was 2011) with composite buffer problems.

Do I miss something or they still problems with the composite buffer? Is there another way to do this that I missed?

Thanks Gatherer

EDIT1: fixed the code example after the first reply

EDIT2: I got it running today. But it’s a little bit weared. I post the real code so I can discribe it better. First the code.

  tvbuff_t *timing_tvb;
timing_tvb = tvb_new_composite();

// I need to calculate the amount of sub buffer I need
// tvb size is calculated before
tvbuff_t *tvb_sub[tvb_size/16/2];
guint loopCounter;
loopCounter = 0;
while(tvb_size > 0) {
tvb_sub[loopCounter] = tvb_new_subset(tvb, payload_offset_save, 16, 32);
tvb_size -= 32;
tvb_composite_append(timing_tvb, tvb_sub[loopCounter]);
// this output is just for testpurpose and shows me that I cut the right data
proto_tree_add_item(tree_reportPayload, hf_proto_hsDebugProtocol_payload_data,          tvb_sub[loopCounter], 0, 16, ENC_BIG_ENDIAN);
// check to see if I go trough the while loop right
printf("loopCounter: %d\n", loopCounter);
payload_offset_save += 32;
loopCounter += 1;
}
tvb_composite_finalize(timing_tvb);
// this line had a testpurpose too but here comes the weired part, I explaine this later
// this is my "special line"
proto_tree_add_item(tree_reportPayload, hf_proto_type_payload_data, timing_tvb, 0, -1, ENC_BIG_ENDIAN);
// call Ethernet
call_dissector(data_handle_eth, timing_tvb, pinfo, tree);

1. When I use the code above it works. I get some strange side effects in column names (e.g. ASSERT erorrs are shown) but its ok. The only problem is that the highligting is completly wrong. The highlighting shows the right amount of bytes but its shown as no cutting happend. E.g. IP shows the right source and destination IP, Port and so on. It’s not pretty but I could live with it.
2. Now the weared part. If I comment out my special line. The Ethernet dissector works fine and calls the IP dissector but then IP dies and throws ASSERT errors and stop dissecting on different. There are some funny things shown like IP Version: 12 but the data is right (4). Any Ideas?